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The equation of state and the crystal structure evolution with pressure were determined for two single crystals of pure natural MgAl 2 O 4 spinels with different degrees of order. The two samples studied were cut from a larger single crystal and one of them was experimentally disordered at high temperature. The two crystals, showing an inversion parameter x of 0.27 and 0.15 at ambient conditions, were loaded together in a diamond anvil cell and their unit-cell edge was measured up to about 7.5 GPa at 14 different pressures. The unit-cell volume, V 0 , the bulk modulus, K T0 , and its first pressure derivative, K ′, were simultaneously refined using a third-order Birch-Murnaghan equation of state, giving the following coefficients: V 0 = 529.32(2) A 3 , K T0 = 193(1) GPa, K ′ = 5.6(3) for the ordered sample and V 0 = 528.39(2) A 3 , K T0 = 192(1) GPa, K ′ = 5.4(3) for the disordered one. Complete intensity data were collected at 0, 0.44, 2.92, 7.34, and 8.03 GPa in a separate experiment. For the ordered and disordered samples the oxygen atomic coordinate u remains practically unchanged inside the investigated pressure range with an average value of 0.2633(5) and 0.2614(2), respectively. As a consequence, the polyhedral compressibilities are similar and are not influenced by the Mg/Al distribution over the two crystallographic sites. This also suggests that pressure has little or no influence on the degree of order in the MgAl 2 O 4 spinel.

Augite and diopside crystals from the Oligo-Miocene high-Mg and high-Al basalts, basaltic andesites and andesites of Montresta (Sardinia, Italy) have been analysed by means of X-ray single crystal diffraction and electron microprobe. It has been found that crystallization or equilibration processes took place within the crust at pressures below 5 kbar. In particular, samples from high-Al basalts, basaltic andesites and andesites crystallised at pressures below one kbar while those from high-Mg basalts crystallised in a range from about 1.5 to 4.5 kbar. The intracrystalline temperatures range between about 550 °C for high-Mg basalts and 750 °C for andesites. The M20 site is occupied in each of the studied crystals, which implies slow cooling rates.

The uncommon sulfide djerfisherite, ideally K6(Fe,Cu,Ni)25S26Cl, occurs in the dunite portion of the Guli complex, located in Polar Siberia, Russia. Distinctive features of the Guli complex are its considerable size, ~2000 km2, making it the largest dunite–clinopyroxenite massif in the world, and its complicated geology. The exposed part is composed predominantly (60%) of variably serpentinized dunite. Melanocratic alkaline rocks cover about 30%, and other rock types, including melilitolite, ijolite, alkaline syenite and carbonatite, occupy less than 10% of the area. The sample with the most abundant djerfisherite is a coarse-grained phlogopite–magnetite-rich clinopyroxenite. Djerfisherite most commonly occurs in irregular patches of sulfide composed mainly of pyrrhotite accompanied by minor chalcopyrite and rare galena, in a matrix of Ti-bearing andradite, clinopyroxene, phlogopite, plagioclase, apatite and rare zircon, titanite and pyrophanite. It forms crystals generally less than 100 µm in size and occurs as irregular single-phase grains or it fills fissures of the silicate matrix and infiltrates phlogopite along its cleavage planes. We provide new data on the physical and crystallographic properties of djerfisherite. Its composition is characterized by an extensive substitution among Fe, Cu and Ni; their reciprocal substitutions are mainly controlled by the nature of the host rock. The djerfisherite from the Guli complex is Cu-rich and resembles that reported from alkaline rocks. This feature is consistent with the proposal that djerfisherite in the Guli complex crystallized as a primary mineral, during the late-stage fractionation of a highly alkaline melt portion, derived from successive fractional melting of an ascending mantle plume under metasomatic conditions.

Crystal chemistry and structural refinement of 20 chromite crystals representative of different chromitites layers and xenoliths from the Critical Zone of the Bushveld Complex have been studied. Small differences in the structural parameters of chromites have been found along the Bushveld sequence and these allowed to discriminate two main subdivision between the Lower and Middle Group samples and the Upper Group and Merensky Reef samples. The small increase of chromite oxygen coordinates seems to be related with the decrease of cooling rates as estimated from the filling and cooling model for the Bushveld Complex proposed by Cawthorn & Walraven (1998). In fact, the cooling rates for Upper Group and Merensky Reef are smaller than that of Lower Group and Middle Group. Moreover, peculiar structural parameters have been found for chromites in the Tweefontein pipe suggesting different cooling rates.

The purpose of this preliminary study was to investigate the physico-chemical properties of nimesulide precipitated by continuous supercritical antisolvent (SAS) from different organic solvents like acetone, chloroform and dichloromethane at 40 degrees C and 80, 85 and 88 bar, respectively. Scanning electron microscopy, differential scanning calorimetry, X-Ray diffractometry and in vitro dissolution tests were employed to study how the technological process and the solvent nature would affect the final product. SAS-processed nimesulide particles showed dramatic morphological change in crystalline structure if compared to native nimesulide, resulting in needle and thin rods shaped crystals. The solid state analysis showed that using chloroform or dichloromethane as a solvent the drug solid state remained substantially unchanged, whilst if using acetone the applied method caused a transition from the starting form I to the meta-stable form II. So as to identify which process was responsible for this result, nimesulide was further precipitated from the same solvent by conventional evaporation method (RV-sample). On the basis of this comparison, the solvent was found to be responsible for the re-organization into the different polymorphic form and the potential of the SAS process to produce micronic needle shaped particles, with an enhanced dissolution rate if compared to the to the pure drug, was ascertained. Finally, the stability of the nimesulide form II, checked by DSC analysis, was ruled on over a period of 15 months.

Several controlled release systems of drugs have been elaborated using a supercritical fluid process. Indeed, recent techniques using a supercritical fluid as a solvent or as an antisolvent are considered to be useful alternatives to produce fine powders. In this preliminary study, the effect of Supercritical Anti Solvent process (SAS) on the release of theophylline from matrices manufactured with hydroxypropylmethylcellulose (HPMC) was investigated. Two grades of HPMC (HPMC E5 and K100) as carriers were considered in order to prepare a sustained delivery system for theophylline which was used as a model drug. The characterization of the drug before and after SAS treatment, and the coprecipitates with carriers, was performed by X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). The dissolution rate of theophylline, theophylline-coprecipitates, and matricial tablets prepared with coprecipitates were determined. The physical characterizations revealed a substantial correspondence of the drug solid state before and after supercritical fluid treatment while drug-polymer interactions in the SAS-coprecipitates were attested. The dissolution studies of the matrices prepared compressing the coprecipitated systems showed that the matrices based on HPMC K100 were able to promote a sustained release of the drug. Further, this advantageous dissolution performance was found to be substantially independent of the pH of the medium. The comparison with the matrices prepared with untreated substances demonstrated that matrices obtained with SAS technique can provide a slower theophylline release rate. A new mathematical model describing the in vitro dissolution kinetics was proposed and successfully tested on these systems.

The influence on the spinel structure of Fe3+ → Cr substitution was studied in flux-grown synthetic single crystals of the magnesiochromite–magnesioferrite (MgCr2O4–MgFe2O4) solid solution series. Samples were analysed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption and Mossbauer spectroscopy. With the exception of iron-poor samples (3–12 mol-% MgFe2O4), optical absorption and Mossbauer spectra show that iron occurs almost exclusively as trivalent Fe in the present samples. A very intense and broad absorption band at ca 7,800 cm−1 dominates the optical absorption spectra of samples with higher Fe-contents. The appearance of this band is related to a distinct structural disorder of Fe3+ and a development of magnetic ordering as demonstrated by Mossbauer spectra. Profound composition-related changes are observed in the Mossbauer spectra, which are magnetically unsplit in the range 2–41 mol-% magnesioferrite, but become magnetically split in the range 59–100 mol-% magnesioferrite. Structural parameters a 0 and M–O increase with magnesioferrite content and inversion degree, while u and T–O decrease. Our study confirms the previously reported (Lavina et al. 2002) influence of Fe3+ at the M site on T–O bond lengths in the spinel structure.

Chromian spinel is a common heavy mineral in the fl ysch basins of the southeastern Alps and Outer Dinarides. Various tectonic settings have been found for the suites of chromian spinel studied herein, related to suprasubduction for both Internal and Outer Dinarides, and ocean-fl oor-spreading zones for the Outer Dinarides. Because the composition of the chromian spinel cannot discriminate between the two areas, we performed crystallochemical studies in order to fi nd some differences. These studies show that it is possible to discriminate between the suprasubduction zones of the Outer and Inner Dinarides by means of the positional parameter u of the oxygen atom, which is close to 0.2625 for spinel grains from Outer Dinarides and greater than 0.2626 for spinel grains from Inner Dinarides. Intracrystalline temperatures ranging from 790 to 1050°C have been calculated for spinels with u close to 0.2625, and 730 to 750°C for those with u higher than 0.2626. These temperatures are consistent with those calculated for Outer and Inner Dinarides, respectively.

The influence on the structure of Fe2+, Mg substitution was studied in synthetic single crystals belonging to the MgCr2O4–FeCr2O4 series produced by flux growth at 900–1200 C in controlled atmosphere. Samples were analyzed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption-, infrared- and Moessbauer spectroscopy. The Moessbauer data show that iron occurs almost exclusively as IVFe2+. Only minor Fe3+ (

The purpose of this study was to investigate the influence of supercritical CO2 processing on the physico-chemical properties of carbamazepine, a poorly soluble drug. Using the gas anti-solvent (GAS) technique, this drug was precipitated from three different solvents (acetone, ethylacetate and dichloromethane) to study, in addition, the effect of these vehicles on the properties of the final product. The samples were analysed before and after treatment by scanning electron microscopy analysis (SEM) and laser granulometer for possible changes in the appearance of the crystals. Furthermore, the solid state of the samples was studied by means of X-Ray powder diffraction (XRD), differential scanning calorimetry (DSC), diffuse reflectance Fourier-transform infrared spectroscopy (DRIFT) and hot stage microscopy (HSM). Finally, the in vitro dissolution tests were carried out. The solid state analysis of treated and untreated with CO2 samples, illustrated that the applied methodology caused a transition from the starting form I to the form I as well as a dramatic change on crystal morphology, resulting in a final product mainly consisting of needle-shaped crystals, regardless of the chosen solvent. Furthermore, to investigate whether this phenomenon was due to the GAS process or the vehicles used, carbamazepine was precipitated from the same three solvents by traditional evaporation method (RV-samples). On the basis of this comparison, the solvents used were found to be responsible for the reorganisation into a different polymorphic form, whereas the potential of the GAS process to produce micronic needle shaped particles, having a enhanced dissolution rate compared to the RV-carbamazepine, was stated.

It is well known that carriers can affect the dissolution of poorly soluble drugs. In this study, our aim was to investigate the dissolution enhancement of carbamazepine solid dispersed or mixed at different loading ratios in crospovidone, polyvinylpyrrolidone, and sodium starch glycolate. The physical state of the drug and the drug-polymer interactions in the solid state were investigated using differential scanning calorimetry (DSC) and x-ray diffraction analysis (XRD). Through the solubilization kinetics and dissolution rates studies, the in vitro drug availability of the systems was evaluated. An improved in vitro dissolution of the drug was obtained in all the binary systems that increased as the polymer content increased.

The Nemby mantle xenoliths are represented by spinel peridotites variably affected by “metasomatic processes” in Proterozoic times (1.2–0.5 Ga). Clinopyroxene compositional variations mainly reflect variably degrees of basalt extraction and mantle “metasomatic processes”. Clinopyroxene crystal chemistry allows to estimate the equilibration pressure by V(Cell) and V(M1) relationship. The investigated clinopyroxenes yielded a pressure range of 12–18 kb. Therefore, the Nemby xenoliths are representative of about 20 km thickness of subcontinental lithospheric mantle of the South America platform at Tertiary times (ca. 46 Ma).

A characterization has been carried out on the dihydrate and anhydrous crystalline form of trehalose (α-d-Glucopyranosyl-α-d-glucopyranoside), which is considered anomalous in respect to other disaccharides in conferring to organisms the ability to be dried at high temperatures and then to rehydrate without damaging cellular functions. The thermal dehydration of the dihydrate trehalose, Th, has been studied with the aim to rationalize the stability and the kinetically controlled transformations of Th into the anhydrous forms. This has been reached by carrying out the dehydration process at different scan rates and by preparing the several polymorphic species. A description is therefore presented of the water−trehalose interaction which controls the thermal stability (or metastability) of the several forms obtained under controlled water depletion. Enthalpy changes and temperatures of transition are also reported and compared with literature data.

The comparative compressibilities of two clinopyroxenes from mantle nodules were determined by single crystal X-ray diffraction with a Merrill-Bassett diamond anvil cell. The analysed crystals show different chemical compositions: PC 135, from a spinel lherzolitic nodule from Pico Cabugi, NE Brazil, has more R3+ (Fe3+ + VIA1 + Ti + Cr) in the Ml site, more Mg in the M2 site (i.e. lower Ca) and more Al in T compared with 3211, a crystal from a spinel harzburgitic nodule from Nemby, Paraguay. Lattice parameters were determined under different pressures between 1 bar and 46 kbar with both crystals mounted together in the diamond anvil cell. The different chemistries of the two samples produce opposite effects on the polyhedral bulk moduli. On the whole, the bulk modulus is the same in both samples: K is 1170(50) kbar in PC 135 and 1160(30) kbar in 3211. For both clinopyroxenes ß/> > ßc > ßαsinß. In particular, the following values were recorded: ß*> = 3.9(7) 10"4, ßc = 2.9(2) 10Λ ßαsin ß = 2.2(6) 10"4 kbar1 in PC135 and ft, = 3.9(8) 104, ßc = 2.7(2) 10'4, ßΩsin ß = 2.5(3) 10-4 kbar1 in 3211. Greater differences are seen in the 81/83 ratios between the semiaxes of the strain ellipsoid of the two clinopyroxenes: the higher content of R3+ in the Ml site and the lower Ca content in the M2 site of PC 135 compared to 3211 produces a more eccentric (010) section of the strain ellipsoid in PC 135 than in 3211. The pressure induced effects of composition on the geometrical deformations are in accordance with those simulated by theoretical calculations.

The relationships between kinking of the T tetrahedral chain and the site configuration of C2/c pyroxenes from volcanic rocks were investigated, and about two hundred samples were examinated.

Mercier's thermobarometer (Mercier 1980) and Saxena's thermometer (Dal Negro et al. 1982) were applied to single pyroxenes of both porphyroclastic (PF) and protogranular (PR) spinel peridotitic nodules enclosed in alkaline products related to necks of North-Eastern Brazil. Intercrystalline temperatures obtained using both orthopyroxene (opx) and clinopyroxene (cpx) compositions were in agreement, and were lower in protogranular than in porphyroclastic nodules (1051_+57 and 1266 +_ 19~ respectively). In contrast, pressure estimates using cpx and opx were conflicting, in particular as regards PF nodules. In fact for PF nodules cpx compositions point to 27 32 kbar (mean 29_+2) whereas opx compositions point to 1%19 kbar (mean 18_+ 1). Conversely, PR nodule cpx and opx compositions point to similar values 17 24 and 15-18 kbar respectively (mean 19_+4). The result obtained for PF nodules using cpx composition clearly contrasts with petrographic evidence and it is due to the peculiar composition of PF cpx (e.g. low Ca content, from 0.645 to 0.737 atoms per formula unit, a.f.u.) that strongly affects the barometric formulation. The PR and PF cpxs reveal similar mean intracrystalline temperature estimates (712 _+ 112 and 778 +_ 217~ respectively). These, considering the difference of about 200~ in the intercrystalline temperature estimates, indicate that the exchange cation reaction between the M1 and M2 sites was a faster process in PF than in PR cpx, favoured by the low Ca content of PF cpx. Thus alternatively, the composition of PF cpx, characterized by a high rate of Ca ~ Mg substitution in the M2 site, may not affect the intercrystalline temperature. Therefore the difference of about 200~ found in intercrystalline temperatures between PR and PF cpxs, in spite of their same pressure values, may be interpreted as indicating an anomalous temperature gradient in the region.

X-ray crystal structure refinements and microprobe analyses of clinopyroxenes from two suites of spinel-peridotite nodules are compared for an understanding of the structural response to a decrease in Ca content. The kinking of the tetrahedral chain (O3-O3-O3 angle) of the C2/c structure associated with decreased Ca content shows behavior similar to that observed for the A-tetrahedral chain of the P21/c structure. Contemporaneously the occupancy of the M2′ split site increases. In addition, as a consequence of the low Ca content, the M2 polyhedron dominates the structural rearrangement of the clinopyroxenes considered here.

A series of clinopyroxenes (Cpx) in peridotitic spinel nodules from Rio Grande do Norte, North-Eastern Brazil, was investigated by X-ray diffraction and electron microprobe analyses and compared with an analogous series from spinel peridotite nodules from Mt. Leura, Victoria, Australia. The examined Cpx series is mainly characterized by increasing Mg/(Mg+Fe2+) ratio (i.e. increase of refractory character of the host nodules), by the substitutions of Alvi vs Mg in the M1 site and Na vs (Ca+Mg) in the M2 site, whereas Aliv in the T site remains substantially constant. The strong Na depletion in the Brazilian Cpx causes a different charge balance from that in the Australian Cpx, in which Na remains quite constant. This feature, associated with the differences in polyhedral and cell volumes which are significantly higher in the Brazilian Cpx than in those of the Australian Cpx, suggests that the Brazilian Cpx crystal chemistry may be related to a lower pressure regime, compared with that of the Australian Cpx series.

The crystal structures of two natural magnetites were refined. Both turned out to have equipoints 8a and 16d (Fd3m) fully occupied and hence different from type I and type II defect structures investigated by Fleet (1981, 1982). It was possible to improve the cation radii for Fe2+ ad Fe3+ in octahedral and tetrahedral coordinations for pure and almost pure magnetites obtaining very good agreement between observed and calculated values of the two independent geometric structure parameters, i.e. cell edge and oxygen coordinate. The present results lead to an estimate of inversion parameter i in (Fe 1− 2+ Fe 3+ )(Fe 2+ Fe 2t- 3+ )O4, of about 0.90, equal for all the four pure magnetites, independently of type of structure and also of cooling history.

Microprobe analyses and X-ray crystal structure refinement data of Mg-Fe-Al-Cr spinels from different environments are compared. The investigated crystals represent both restitic and recrystallized spinels from an Alpine peridotitic massif, and restitic spinels from four suites of ultramafic xenoliths. Within each suite the crystals represent different steps of an increasing melting process, which causes a strong increase in Cr3+ and a moderate increase in Fe2+, with depletion of Al3+ and Mg2+. Within each suite, in spite of relevant bulk chemistry changes, the ratio of the octahedral to tetrahedral coordination distances, and consequently the oxygen positional parameterx, are kept constant. Conversely,x may differ in suites with similar bulk chemistry, mainly due to different Mg-Al ordering between octahedral and tetrahedral sites. This suggests that thex parameter is strongly affected by physical environment, and that consequently, within the range of the investigated compositions, it could be used as a marker.

On the basis of whole-rock and mineral chemistry two main magmatic groups can be established for the Paleozoic Volcanism of the Carnian Alps. High-Ti Volcanics (HTV) and Low-Ti Volcanics (LTV). Spilitization processes have not masked the primary magmatic character. The two groups are characterized by very different trace element patterns and cannot be correlated by a fractionation process. The HTV require an enriched mantle source whereas the geochemistry of the LTV indicates strong crustal contamination. Both magmatic groups are consistent with a major rifting episode. The contamination via assimilation of crustal rocks of the LTV group implies that rifting developed in a continental area.

Textural-petrographic features, major and trace elements and mineral chemistry are reported for spinel-peridotite xenoliths from northeastern Brazil (NE-suite) and Paraguay (PY-suite). Variation trends defined by bulk rock and mineral chemistry are consistent with the effects of variable degree of high-pressure melting for both suites. The PY-suite strongly differs from the NE-suite by its very high contents of incompatible elements. This different whole-rock chemistry is related to the presence of glassy-microcrystalline blebs which are interpreted as remains of pre-existing hydrous phases of metasomatic origin. The difference between the two suites is also recorded in the chemistry of pyroxenes and spinels, which develop along different variation patterns. Although the suites partially overlap in their ranges of mg opx (Mg/(Fe 2+ + Fe 3+ ) ratio in orthopyroxenes), the PY-suite is, on the average, more mg opx rich (residual) than the NE-suite. Within the PY-suite a rough positive correlation exists between degree of residuality and degree of metasomatic effects. The sharp differences between the NE-suite and the PY-suite imply mantle heterogeneity on regional scale, whereas the variability within each suite is essentially related to different degrees of melting and/or metasomatism and imply mantle heterogeneity on local scale.

The results of the present paper confirm the overall dependence of the geometric parameters of olivines on the Mg/(Fe+Mn) ratio. M1 and M2 volumes linearly decrease with increasing forsterite (Fo) content but at different rates. The difference between the volumes of the octahedral sites decreases gradually fromFo 92% toFo 50% and then remains virtually constant down toFo 0.2%. Fe(M1)/Fe(M2) ratios indicate that Fe2+ prefers the M1 site in fayalite (Fa)-rich olivines (Fa=39% to 92%; average Fe(M1)/Fe(M2)=1.04±0.02). Instead, in Mg-olivines (Fo=80% to 92%) a Mg-M1 preference (average Mg(M1)/Mg(M2)=0.96±0.05) may exist. Finally, Mn(M1)/Mn(M2) ratios do not indicate a definite Mn preference for M2 in the studied olivines (MnO=0.44% to 4.5 wt.%; average Mn(M1)/Mn(M2)=0.99±0.13). No relevant influence on geometric parameters was observed between Ca-free and Cabearing (maximum CaO=0.66 wt.%) olivines.

In the Nuggihalli schist belt (India), chromite bodies were affected by intense serpentinization followed by weathering. In spite of the strong oxidation of the chromite grains, some unaltered cores were preserved, and they were characterised using electron probe microanalysis, single-crystal X-ray diffraction and low temperature 57Fe Mossbauer spectroscopy. Results of such investigations revealed that chromite cores from the Nuggihalli schist belt are effectively not oxidised, and their study revealed that chromite was not affected by greenschist-facies metamorphism. The apparently highly ordered cation distribution of the chromites, which would suggest low equilibration temperature, is just caused by the very high Cr contents, which prevent Mg–Al exchange between T and M sites. Using Fabries (1979) geothermometer a temperature of about 1180 °C was retrieved (Mitra and Bidyananda, 2003), which therefore corresponds to the quenched-in igneous equilibrium.